The present invention relates to methods and apparatuses for automated manufacture of a reclosable plastic package having a resealable closure, especially as part of a form, fill and seal process. In particular, the invention relates to methods and apparatuses for manufacturing reclosable plastic packages and bags having a slider-zipper assembly installed in the mouth of the package.
In the use of plastic bags and packages, particularly for foodstuffs, it is important that the bag be hermetically sealed until the purchaser acquires the product, takes it home, and opens the bag or package for the first time. It is then commercially attractive and useful for the consumer that the bag or package be reclosable so that its contents may be protected. Flexible plastic zippers have proven to be excellent for reclosable bags, because they may be manufactured with high-speed equipment and are reliable for repeated reuse.
A typical zipper comprises one fastener strip or member having a groove and attached to one side of the bag mouth, and another fastener strip or member having a rib and attached to the other side of the bag mouth, which rib may interlock into the groove when the sides of the mouth of the bag are pressed together. Alternatively, a fastener strip having a plurality of ribs may be on one side of the bag mouth, while a fastener strip having a plurality of grooves or channels may be on the other side, the ribs locking into the channels when the sides of the mouth of the bag are pressed together. In the latter case, there may be no difference in appearance between the two fastener strips, as the ribs may simply be the intervals between channels on a strip that may lock into another of the same kind. In general, and in short, some form of male/female interengagement is used to join the two sides of the bag mouth together. The fastener strips or members are bonded in some manner to the material from which the bags themselves are manufactured.
In the automated manufacture of plastic reclosable packages or bags, it is known to feed a zipper assembly to a position adjacent a sheet of thermoplastic film and then attach the zipper assembly to the bag by means of heat sealing. The zipper assemblies are attached at spaced intervals along the thermoplastic sheet, one zipper assembly being attached to each section of film respectively corresponding to an individual package or bag. The zipper assembly consists of two interlocking fastener strips that, in the final package, lie inside the mouth of the package. Each fastener strip preferably has a flange that extends toward the product side of the package in a direction transverse to the line of the zipper. In accordance with one known method of feeding zipper assemblies to an automated form, fill and seal machine, the zipper assembly is in the form of a tape that is unwound from a spool for automated feeding. The tape comprises a continuous length of interlocked fastener strips. The continuous tape is feed to a cutting device that cuts the tape at regular lengths to form an individual zipper. Each individual zipper is attached to the thermoplastic film by heat sealing or other suitable means.
Prior to cutting and heat sealing, the zipper assembly must be automatically positioned correctly relative to the thermoplastic film. Moving the zipper assembly into position overlying the thermoplastic film requires a positioning device. Some prior art positioning devices comprise a channel that guides the continuous zipper tape toward its proper position relative to the thermoplastic bag making film. The zipper assembly may be positioned parallel or perpendicular to the direction of movement of the bag making film. Because the fastener strips of a zipper assembly not slider-operated have a constant profile in the lengthwise direction, it is a relatively simple matter to design a linear guide channel having a cross section which matches the profile of the interlocked fastener strips with sufficient clearance to allow the zipper tape to be pushed or pulled through the guide with minimal friction, yet not so great as to allow the zipper tape to skew, twist or move sideways in the guide channel.
Other types of reclosable plastic bags, however, contain a slider that facilitates a consumer opening and re-closing the package by disengaging and re-engaging the two sides of the zipper. However, adding a slider to the zipper assembly requires the design of guide devices different than those used when reclosable packages having zippers without sliders are being manufactured.
In the prior art it is known to feed a continuous tape of interlocked faster strips to a shaping device that crushes the strips at regular intervals in the lengthwise direction to provide restraints or stops for the slider. At the next station, a slider insertion device inserts a respective slider onto each section of zipper tape between successive slider end stops. The slider can be slid along the zipper tape between a leftmost position in abutment with the left-hand slider end stop and a rightmost position in abutment with the right-hand slider end stop. The resulting tape of slider-zipper assemblies must be fed automatically to a station where each slider-zipper assembly will be cut off the end of the tape and attached to a respective section of the thermoplastic bag material, e.g., by heat sealing, such sections of thermoplastic bag material being spaced at package intervals.
There is a need for a method and an apparatus for guiding a tape of slider-zipper assemblies to a desired position overlying the bag making film during automated feeding of the slider-zipper assemblies. The apparatus must take into account that the sliders intermittently placed along the continuous zipper tape have width and height dimensions greater than the corresponding dimensions of the interlocked profiles of the zipper halves.